This invention relates to a local telephone system tamper protection device. In particular, it is directed to be used with a conventional security alarm system, which may utilize an automatic telephone dialer to call a central monitoring system.
Prior art in this field, such as the literature on line cut monitors or cellular phone backup systems, have established the fact that conventional security alarm systems, which utilize automatic telephone dialers to call a central monitoring station, are rendered useless when a land based telephone line is cut. The telephone service lines are generally such that the telephone service line is easily to access by an intruder from the exterior of the structure being served.
Cellular backup systems for a standard security alarm system are disclosed in U.S. Pat. Nos. 4,887,290 and 5,185,779. An automatic switching to the cellular system occurs so that a digital communicator or telephone message tape dialer will still transmit a distress call to a central alarm monitor. A line default detector means will cause the telephone system to switch over to the cellular system in response to the fault. The cellular systems will not prevent the fault in the first place, but only reports its occurrence. A cellular backup system, which will take over for an inoperative land based phone line, adds to the installation expense of an alarm system, and a continuing monthly charge for the cellular system may be required.
Line cut monitor systems have addressed the problem by providing a detection device for notification that a line has been cut. These systems typically monitor line voltage and current with a circuit connected to a battery or DC-rectified AC power source. Typical references include U.S. Pat. Nos. 3,748,389; 3,767,867; and 4,969,178. In U.S. Pat No. 3,748,389 the monitoring system measures impedance between conductors having a DC polarity. A low impedance as well as a high impedance alarm responds to the open circuit or the closed circuit to indicate to the central office that an alarm condition exists at a subscribers set. A field effects transmitter is disclosed in U.S. Pat. No. 3,767,867 to relay the alarm activated by cutting a telephone wire. There is also a panic button in this system which may be activated for turning on manually the alarm. The panic button depends on the occupant of the structure knowing the intruder is present. The invention of U.S. Pat. No. 4,969,178 uses a voltage detection circuit, a current detection circuit, two control circuits and a comparator circuit to detect breaking, short-circuit or illegal connection of the subscriber local line. An alarm circuit and a sound generating circuit give a audio alarm signal when the local line fails. All of the line cut monitors effectively leave an occupant of the structure virtually defenseless in so far as having any means to telephone for help.
A switch activated alarm system to monitor vandalism is disclosed in U.S. Pat. No. 3,813,500. This alarm system is used with vending machines or pay-station telephones to monitor and control their usage. Contacts of a switch device are coupled with a high-value resistor to make up a leakage path. Current flowing through the leakage path also flows in a low-value resistor which is part of the alarm system circuit. The alarm circuit bridges the talking circuit making the system virtually transparent to a telephone subscriber. An important object of this system is to disable the pay-station or vending machine once vandalism has been attempted. No attempt is made to keep the systems operating once an attempt to vandalize is apparently being made.
The use of tamper switches is common in alarm systems to detect the opening of a window or a door. Further components include motion sensors, heat sensors and video cameras. Such components are normally reserved for commercial structures such as banks and can become expensive for the individual home owner. The use of vibration sensors with telephone line transmission of signals has also been used in special applications. For example, in U.S. Pat. No. 4,559,828 and French Patent No. 2,605,170 the continuous monitoring of machine vibrations is disclosed. The vibration signals are transmitted over telephone lines to a monitoring station for evaluation. These systems operate to continuously monitor vibrations and operate as a closed circuit at all times.
Tamper switches and other sensor devices can be connected in paralles or in series. The disclosure of U.S. Pat. No. 4,361,833 details two normal configurations which are either closed or open loop circuits as well as a "multiple-contact" sensor configuration. The alarm system of this patent can recondition itself by supervising the status of the sensors in the circuit path. Such systems are used with complex alarm systems having many sensors types which can be remotely located.
A primary object of the present invention is to provide protection from tampering for an exposed portion of a local telephone line as it enters a structure.
Another object of the present invention is to provide an alarm for processing (by a control unit of a conventional security alarm system) in the event of an attempt being initiated by an intruder to tamper with the local telephone line as it enters the structure and before a successful entry can be achieved.
Yet another object of the present invention is to have a generally affordable alternative to alarm system tampering which can be easily added to the already existing system to improve the protection afforded by the existing system by guarding against normal telephone communication failure.